Gate structure of vertical FET and method of manufacturing the same

ABSTRACT

A vertical field-effect transistor (VFET) includes: a fin structure on a substrate; a gate structure including a gate dielectric layer on an upper portion of a sidewall of the fin structure, and a conductor layer on a lower portion of the gate dielectric layer; a top source/drain (S/D) region above the fin structure and the gate structure; a bottom S/D region below the fin structure and the gate structure; a top spacer on an upper portion of the gate dielectric layer, and between the top S/D region and a top surface of the conductor layer; and a bottom spacer between the gate structure and the bottom S/D region. A top surface of the gate dielectric layer is positioned at the same or substantially same height as or positioned lower than a top surface of the top spacer, and higher than the top surface of the conductor layer.

CROSS-REFERENCE TO THE RELATED APPLICATION

This is a continuation application of U.S. application Ser. No.16/828,049 filed Mar. 24, 2020, which claims priority from U.S.Provisional Application No. 62/846,153 filed on May 10, 2019, in theU.S. Patent and Trademark Office, the disclosures of which areincorporated herein in their entirety by reference.

BACKGROUND 1. Field

Apparatuses consistent with exemplary embodiments of the inventiveconcept relate to a vertical field effect transistor (VFET).

2. Description of the Related Art

It is known that a VFET has advantages in scale over a conventionalplanar field effect transistor (FET) because a more reduced size of asemiconductor cell can be designed and manufactured.

As known, the VFET is characterized in that a vertical fin structure isformed above a substrate, and a top source/drain (S/D) region and abottom S/D region are formed above and below the fin structure,respectively. Further, a gate structure is formed along sidewalls of thefin structure to surround the fin structure. Like in a planar FET, thegate structure of the VFET receiving an input signal to activate theVFET, and gate controllability thereof are factors to improve the entireVFET performance.

Accordingly, improved technologies and techniques for forming the gatestructure of the VFET would be desirable.

SUMMARY

Various embodiments of the inventive concept are directed to a verticalfield effect transistor (VFET) device and a method of manufacturing theVFET device.

These embodiments may provide VFET devices having improved performanceof a gate structure and methods to achieve the improved VFET devices.

According to exemplary embodiments, there is provided a VFET devicewhich may include: a fin structure formed on a substrate; a gatestructure including a gate dielectric layer formed on an upper portionof a sidewall of the fin structure, and a conductor layer formed on alower portion of the gate dielectric layer; a top source/drain (S/D)region formed above the fin structure and the gate structure; a bottomS/D region formed below the fin structure and the gate structure; a topspacer formed on an upper portion of the gate dielectric layer, andbetween the top S/D region and a top surface of the conductor layer; anda bottom spacer formed between the gate structure and the bottom S/Dregion. Top surface of the gate dielectric layer is positioned at thesame or substantially same height as or positioned lower than a topsurface of the top spacer, and higher than the top surface of theconductor layer.

According to exemplary embodiments, there is provided a VFET devicewhich may include: a fin structure formed on a substrate; a gatestructure including a gate dielectric layer formed on an upper portionof a sidewall of the fin structure, and a conductor layer formed on alower portion of the gate dielectric layer; a top source/drain (S/D)region formed above the fin structure to cover the gate structure; abottom S/D region formed below the fin structure and the gate structure;an interlayer formed outside the gate structure and the top S/D region;an air gap spacer formed between the top S/D region and a top surface ofthe conductor layer of the gate structure, and between the gatestructure and the interlayer; and a bottom spacer formed between thegate structure and the bottom S/D region.

According to exemplary embodiments, there is provided a method ofmanufacturing a VFET device. The method may include: providing a stackof a bottoms S/D region, a fin structure, and a gate structure on a sidewall of the fin structure, an interlayer on a sidewall of the gatestructure, and a mask layer on the fin structure, the stack furtherincluding a bottom spacer on the bottom S/D region and below the gatestructure and the interlayer, and the gate structure comprising a gatedielectric layer on the sidewall of the fin structure and a conductorlayer on the gate dielectric layer; etching the stack from a top surfacethereof to remove the gate dielectric layer and the conductor layer, bydifferent depths from the top surface thereof, and the mask layer toleave an upper portion of the gate dielectric layer and the finstructure such that the upper portion of the gate dielectric layer ispositioned above a plane where a top surface of the conductor layer ispositioned; and forming a top S/D region on the top surface of the finstructure, the top surface of the gate structure and a sidewall of theinterlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of inventive concepts will become moreapparent to those of ordinary skill in the art by describing in detailexample embodiments thereof with reference to the accompanying drawings,in which:

FIGS. 1A to 1C illustrate a process of manufacturing a VFET according toan exemplary embodiment;

FIGS. 2A to 2C illustrate a process of manufacturing a VFET according toanother exemplary embodiment;

FIGS. 3A to 3C illustrate a process of manufacturing a VFET according tostill another exemplary embodiment; and

FIGS. 4A to 4C illustrate a process of manufacturing a VFET according toyet another exemplary embodiment.

DETAILED DESCRIPTION

Various embodiments of the inventive concept will be described morefully hereinafter with reference to the accompanying drawings. Theseembodiments are all exemplary, and may be embodied in many differentforms and should not be construed as limiting the inventive concept.Rather, these embodiments are merely provided so that this disclosurewill be thorough and complete, and will fully convey the inventiveconcept to those skilled in the art. In the drawings, the sizes andrelative sizes of the various layers and regions may have beenexaggerated for clarity, and thus, the drawings are not necessarily toscale, some features may be exaggerated to show details of particularcomponents or elements. Therefore, specific structural and functionaldetails disclosed herein are not to be interpreted as limiting, butmerely as a representative basis for teaching one skilled in the art tovariously employ the methods and structures of the embodiments.

An embodiment provided herein is not excluded from being associated withone or more features of another example or another embodiment alsoprovided herein or not provided herein but consistent with the inventiveconcept. For example, even if matters described in a specific embodimentare not described in a different embodiment, the matters may beunderstood as being related to or combined with the differentembodiment, unless otherwise mentioned in descriptions thereof.

For the purposes of the description hereinafter, the terms “upper”,“lower”, “top”, “bottom”, “left,” and “right,” and derivatives thereofcan relate, based on context, to the disclosed structures, as they areoriented in the drawings. The same numbers in different drawings mayrefer to the same structural component or element thereof.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list. Thus,for example, both “at least one of A, B, or C” and “A, B, and/or C”means either A, B, C or any combination thereof. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

As used herein, the term “surface” may refer to an end or an end pointof a corresponding element, not being limited thereto a flat plane, andthus, the “surface” may indicate a non-flat area or point. For example,a “top (bottom) surface” may refer to a top (bottom) end or end point ofa corresponding element.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the embodiments belong. It will befurther understood that terms, such as those defined in commonly-useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIGS. 1A to 1C illustrate a process of manufacturing a VFET according toan exemplary embodiment.

First, a semiconductor stack 100 shown in FIG. 1A is provided forfurther processing to complete a VFET. According to an exemplaryembodiment, the semiconductor stack 100 may be provided through achemical-mechanical polishing (CMP) operation which includeschemical-mechanical planarization using chemical reactions. However,methods of providing the semiconductor stack 100 are not limited to aparticular process such as the CMP operation.

The semiconductor stack 100 includes a bottoms S/D region 110 formed ona substrate (not shown), a fin structure 120 formed to become a channelof a VFET, and a gate structure 130 formed on a side wall of the finstructure 120. Here, the gate structure 130 may be conformally formedalong a sidewall of the fin structure 120. The gate structure 130includes at least a gate dielectric layer 131 and a conductor layer 132,and the gate dielectric layer 131 includes at least an interfacial layer131-1 formed on the sidewall of the fin structure 120 and an high-κdielectric layer 131-2 formed on the interfacial layer 131-1. Thesemiconductor stack 100 further includes an interlayer 140 formed on asidewall of the gate structure 130, a mask layer 150 formed on the finstructure 120, and a bottom spacer 160 formed on the bottom S/D region110 and below the gate structure 130 and the interlayer 140.

The fin structure 120 may be formed from a semiconductor epitaxy (orepitaxial layer) which is grown on a substrate (not shown) and formed ofa material such as silicon (Si), germanium (Ge), silicon germanium(SiGe), and/or a silicon-containing material, not being limited thereto.The bottom S/D region 110 may be formed by doping the semiconductorepitaxy with one or more dopants such as boron (B) for a p-channel VFETand phosphorous (P) for n-channel VFET, not being limited thereto.

The interfacial layer 131-1 of the gate dielectric layer 131 may havebeen formed along the sidewall of the fin structure 120 applying atleast one of chemical vapor deposition (CVD), plasma-enhanced CVD(PECVD) and atomic layer deposition (ALD) using at least one materialselected from silicon oxide (SiO), silicon dioxide (SiO₂), and/orsilicon nitride (SiON), not being limited thereto. The interfacial layer131-1 may be provided for not only protecting the fin structure 120 butfacilitating growth of the high-κ dielectric layer 131-2 thereon andproviding a necessary characteristic interface with the fin structure120.

The high-κ dielectric layer 131-2 may be formed of a metal oxidematerial or a metal silicate such as Hf, Al, Zr, La, Mg, Ba, Ti, Pb, ora combination thereof, not being limited thereto, having a dielectricconstant value greater than 7. Preferably but not necessarily, thehigh-κ material may be HfO₂ and/or HfSiON, not being limited thereto,having a dielectric constant value greater than 15. The high-κdielectric layer 131-2 may be provided to allow an increased gatecapacitance without associated current leakage at the gate structure 130in the VFET.

The conductor layer 132 may include a metal or metal compound such asCu, Al, Ti, Ta, W, Co, TiN, WN, TiAl, TiAlN, TaN, TiC, TaC, TiAlC, TaCN,TaSiN, or a combination thereof, not being limited thereto.

One of parameters to affect the performance of the gate structure 130may be the lateral thickness of the gate dielectric layer 131 formedalong the sidewall of the fin structure 120. The smaller is the lateralthickness of the gate dielectric layer 131, the better performance maybe had by the gate structure 130.

The interlayer 140 insulates the VFET from an outside conduction source,and may be formed of nitride, oxide, or a combination thereof, not beinglimited thereto. The mask layer 150 protects the fin structure 120 froman etching operation to be described in a next process of manufacturingthe VFET. Photoresist or silicon nitride (SiN) may be used as maskingmaterial, not being limited thereto.

After providing the semiconductor stack 100 shown in FIG. 1A, thesemiconductor stack 100 is applied an etching operation to remove themask layer 150 and a given portion of the gate structure 130 from a topsurface 130T thereof, thereby leaving only the fin structure 120 by acertain vertical length above a plane where a top surface 130T of thegate structure 130 is positioned between the interlayers 140 as shown inFIG. 1B. Thus, the fin structure 120 at an upper portion 120U takes aform of protrusion from the plane where the top surface 130T of the gatestructure 130 is positioned between the interlayers 140.

According to an exemplary embodiment, the foregoing etching operationapplied to the semiconductor stack 100 may include wet etching toselectively remove specific materials, that is, portions of the gatestructure 130 as well as the mask layer 150 which may be formed of anitride material such as silicon nitride (SiN), not being limitedthereto.

After the etching operation described above, a top spacer 170 and a topS/D region 180 are formed to complete the VFET, as shown in FIG. 1C.

The top spacer 170 is formed above the gate structure 130 and betweenthe fin structure 120 and the interlayers 140 by using at least one ofCVD, PECVD and ALD, not being limited thereto. The top spacer 170 andthe bottom spacer 160 may be formed of a material of at least one ofsilicon oxide (SiO₂), silicon nitride (SiN), and any low-κ materialssuch as SiCOH or SiBCN having a dielectric constant value less than 3.5,not being limited thereto. The top spacer 170 and the bottom spacer 160may be formed of the same or different materials(s), and may serve toelectrically isolate the gate structure 130 from the top S/D region 180and the bottom S/D region 110, respectively.

The top S/D region 180 is formed at a position above the fin structure120 and the top spacer 170 and between the interlayers 140. To form thetop S/D region 180, a semiconductor epitaxy may be grown on the topsurface 120T of the protruded fin structure 120, and then, thesemiconductor epitaxy may be doped with one or more dopants such asboron (B) for a p-channel VFET and phosphorous (P) for n-channel VFET,not being limited thereto.

In this embodiment, however, as shown in FIG. 1C, an upper portion 131Uof the gate dielectric layer 131 became thicker and the conductor layer132 became thinner in a lateral direction from the sidewall of the finstructure 120. That is, the equivalent oxide thickness (EOT) of the gatedielectric layer 131 increases at the upper portion 131U. Thus, the gatedielectric layer 131 is thicker at the upper portion 131U than a lowerportion 131L, and the conductor layer 132 is thinner at an upper portion132U than a lower portion 132L. The inventors of this applicationidentified that this increase of the EOT may be caused because at leastthe interfacial layer 131 formed of the oxide material such as siliconoxide (SiO), silicon dioxide (SiO₂), and/or silicon nitride (SiON) isexposed to air during the follow-on operations to form the VFET, therebyto cause oxidation or reoxidation on a top surface 131T of the gatedielectric layer 131 including the interfacial layer 131-1. Theinventors also learned that the increase of the EOT at the gatedielectric layer 131 adversely affects the performance of the gatestructure 130.

Accordingly, new embodiments are provided in reference to FIGS. 2A to 2Cand 3A to 3C.

FIGS. 2A to 2C illustrate a process of manufacturing a VFET according toanother exemplary embodiment.

Similar to the previous embodiment, the present embodiment begins withproviding a semiconductor stack 200 shown in FIG. 2A through a CMPoperation, not being limited thereto, for further processing to completea VFET. The semiconductor stack 200 includes a bottom S/D region 210, afin structure 220, a gate structure 230 including a gate dielectriclayer 231 and a conductor layer 232, where the gate dielectric layer 232is formed of at least an interfacial layer 231-1 and a high-κ dielectriclayer 231-2. The semiconductor stack 200 further includes an interlayer240, a mask layer 250, and a bottom spacer 260. Since the materials,structures, and functions of the above elements included in thesemiconductor stack 200 may be the same as those included in thesemiconductor stack 100, duplicate descriptions thereabout are omitted.

However, etching and top spacer forming operations described below inreference to FIGS. 2B and 2C differ from those described in reference toFIGS. 1B and 1C.

Referring to FIG. 2B, after the semiconductor stack 200 shown in FIG. 2Ais provided, an etching operation is performed on the semiconductorstack 200 to remove the mask layer 250 and portions of the gatestructure 230. Here, the gate structure 230 is etched such that portionsof the gate dielectric layer 231 and the conductor layer 232 are removedby different depths from a top surface of the gate structure 230 shownin FIG. 2A. In other words, the gate dielectric layer 231 is etched by aless depth than the conductor layer 232, or the conductor layer 232 isetched by a greater depth than the gate dielectric layer 231 so that,after the etching operations, a portion of the gate dielectric layer 231of a certain vertical length (referred to as “an upper portion 231U ofthe gate dielectric layer 231” herebelow) above a plane where a topsurface 232T of the conductor layer 232 is positioned still remains on asidewall 220S of the fin structure 220 at an upper portion 220U thereof.Thus, the upper portion 220U of the fin structure 220 along with theupper portion 231U of the gate dielectric layer 231 take a form ofprotrusion from the plane where the top surface 232T of the conductorlayer 232 is positioned between the interlayers 240. Further, by thisetching operation, a top surface 231T of the gate dielectric layer 231is positioned higher than the top surface 232T of the conductor layer232, and is coplanar or substantially coplanar with a top surface 220Tof the fin structure 220.

Accordingly, the upper portion 231U of the gate dielectric layer 231,where the EOT described in the previous embodiment is likely to increaselaterally, including a portion where the EOT is likely to be thegreatest, due to oxidation or reoxidation, remains above the plane wherethe top surface 232T of the conductor layer 232 is positioned. That is,at a side of the upper portion 231U of the gate dielectric layer 231, noportion of the conductor layer 232 is positioned. Thus, even if the EOTincrease occurs at the upper portion 231U of the gate dielectric layer231, the gate dielectric layer 231 at a lower portion 231L, where theEOT increase does not occur, positioned below the plane where the topsurface 232T of the conductor layer 232 is positioned, may maintain auniformly thin or substantially uniformly thin lateral thickness alongthe sidewall 220S of the fin structure 220, thereby not adverselyaffecting gate controllability.

The etching operation of the present embodiment may also be performed bythe same wet etching performed in the previous embodiment as shown inFIG. 1B. Thus, duplicate descriptions thereabout are omitted.

After the etching operation shown in FIG. 2B, a top spacer 270 and a topS/D region 280 is formed to complete the VFET, as shown in FIG. 2C.Since the materials, structures, and functions of the top spacer 270 andthe top S/D region 280 may be the same as described above in referenceto FIG. 1C, duplicate descriptions thereabout are omitted.

However, unlike the previous embodiment shown in FIG. 1C in which abottom surface of the top spacer 170 contacts an entirety of the topsurface 130T of the gate structure 130 including the gate dielectriclayer 131 and the conductor layer 132, the top spacer 270 of the presentembodiment is formed such that a bottom surface of the top spacer 270 ofthe VFET contacts only the top surface 232T of the conductor layer 232in the gate structure 230. Further, according to the present embodiment,a top surface 270T of the top spacer 270 is coplanar or substantiallycoplanar with the top surface 231T of the gate dielectric layer 231including the interfacial layer 231-1 and the high-κ dielectric layer231-2.

Thus, even if the EOT increases at the upper portion 231U of the gatedielectric layer 231, the upper portion 231U of the gate dielectriclayer 231, where the EOT is increased is positioned vertically insidethe top spacer 270 where the conductor layer 232 is not formed at a sideof the gate dielectric layer 231, and the lateral thicknesses of thelower portion 231L of the gate dielectric layer 231 and the conductorlayer 232 which are positioned vertically outside the top spacer 270 donot change or substantially change along the lower portion 220L of thefin structure 220.

Accordingly, the etching operation and subsequent operations of formingthe top spacer 270 according to the present embodiment may be able toform an improved VFET by preventing performance degradation of the gatestructure 230 which may occur in the previous embodiment.

Meanwhile, the amount of the upper portion 231U of the gate dielectriclayer 231 which is to remain after the etching operation of FIG. 2B maybe determined such that the vertical length of the upper portion 231U ofthe gate dielectric layer 231 where the EOT increases to degrade theperformance of the gate structure 230 can be smaller than or equal tothe vertical thickness of the top spacer 270.

FIGS. 3A to 3C illustrate a process of manufacturing a VFET according tostill another exemplary embodiment.

Similar to the previous embodiments, the present embodiment begins withproviding a semiconductor stack 300 shown in FIG. 3A through a CMPoperation, not being limited thereto, for further processing to completea VFET. The semiconductor stack 300 includes a bottom S/D region 310, afin structure 320, a gate structure 330 including a gate dielectriclayer 331 and a conductor layer 332, where the gate dielectric layer 332is formed of at least an interfacial layer 331-1 and a high-κ dielectriclayer 331-2. The semiconductor stack 300 further includes an interlayer340, a mask layer 350, and a bottom spacer 360. Since the materials,structures, and functions of the above elements included in thesemiconductor stack 300 may be the same as those included in thesemiconductor stacks 100 and 200, duplicate descriptions thereabout areomitted.

However, etching and top spacer forming operations described below inreference to FIGS. 3B and 3C differ from those described in reference toFIGS. 1B, 1C, 2B and 2C.

Referring to FIG. 3B, after the semiconductor stack 300 shown in FIG. 3Ais provided, an etching operation is performed on the semiconductorstack 300 to remove the mask layer 350 and portions of the gatestructure 330. Here, the gate structure 330 is etched such that portionsof the gate dielectric layer 331 and the conductor layer 332 are removedby different depths from a top surface of the gate structure 330 shownin FIG. 3A. In other words, the gate dielectric layer 331 is etched by aless depth than the conductor layer 332, or the conductor layer 332 isetched by a greater depth than the gate dielectric layer 331 so that,after the etching operation, a portion of the gate dielectric layer 331of a certain vertical length (referred to as “an upper portion 331U ofthe gate dielectric layer 331” herebelow) above a plane where a topsurface 332T of the conductor layer 332 is positioned still remains on asidewall 320S of the fin structure 320 at an upper portion 320U thereof.Thus, the upper portion 320U of the fin structure 320 along with theupper portion 331U of the gate dielectric layer 331 take a form ofprotrusion from the plane where the top surface 332T of the conductorlayer 332 is positioned between the interlayers 340.

However, the etching operation according to the present embodiment shownin FIG. 3B differs from the previous embodiment of FIG. 2B in that theamount of the upper portion 331U of the gate dielectric layer 331remaining by the etching operation on the semiconductor stack 300 issmaller than that of the upper portion 231U of the gate dielectric layer231 remaining after the etching operation in the previous embodiment.That is, the vertical length of the upper portion 331U of the gatedielectric layer 331 is smaller than that of the upper portion 320U ofthe fin structure 320 which takes a form of protrusion from the planewhere the top surface 332T of the conductor layer 332 is positioned, andthe top surface 332T of the conductor layer 332 is formed to be lowerthan a top surface 320T of the fin structure 320.

Still, however, the purpose and result of the etching operation of FIG.3B may be the same as those of FIG. 2B. In other words, the upperportion 331U of the gate dielectric layer 331, where the EOT is likelyto increase laterally, including a portion where the EOT is likely to bethe greatest, due to oxidation or reoxidation, remains above the planewhere the top surface 332T of the conductor layer 332 is positioned.That is, at a side of the upper portion 331U of the gate dielectriclayer 331, no portion of the conductor layer 332 is positioned. Thus,even if the EOT increase occurs at the upper portion 331U of the gatedielectric layer 331, the gate dielectric layer 331 at a lower portion331L, where the EOT increase does not occur, positioned below the planewhere the top surface 332T of the conductor layer 332 is positioned, maymaintain a uniformly thin or substantially uniformly thin lateralthickness along the sidewall 320S of the fin structure 320, thereby notadversely affecting gate controllability.

The etching operation of the present embodiment may also be performed bythe same wet etching performed in the previous embodiment as shown inFIGS. 1B and 2B. Thus, duplicate descriptions thereabout are omitted.

After the etching operation shown in FIG. 3B, a top spacer 370 and a topS/D region 380 is formed to complete the VFET, as shown in FIG. 3C.Since the materials, structures, and functions of the top spacer 370 andthe top S/D region 380 may be the same as described above in referenceto FIGS. 1C and 2C, duplicate descriptions thereabout are omitted.

The operation of forming the top spacer 370 according to the presentembodiment shown in FIG. 3C is similar to that performed in the previousembodiment shown in FIG. 2C in that a bottom surface of the top spacer370 of the VFET contacts only the top surface 332T of the conductorlayer 332 in the gate structure 330.

However, unlike the previous embodiment shown in FIG. 2C in which thetop surface 270T of the top spacer 270 is coplanar or substantiallycoplanar with the top surface 231T of the gate dielectric layer 231, thetop spacer 370 of the present embodiment is formed such that a topsurface 370T of the top spacer 370 is positioned higher than a topsurface 331T of the gate dielectric layer 331 including the interfaciallayer 331-1 and the high-κ dielectric layer 331-2.

Thus, even if the EOT increases at the upper portion 331U of the gatedielectric layer 331, the upper portion 331U of the gate dielectriclayer 331, where the EOT is increased is positioned vertically insidethe top spacer 370 where the conductor layer 332 is not formed, and thelateral thicknesses of the lower portion 331L of the gate dielectriclayer 331 and the conductor layer 332 positioned vertically outside thetop spacer 370 do not change or substantially change along the lowerportion 320L of the fin structure 320.

Accordingly, the etching operation and subsequent operations of formingthe top spacer 370 according to the present embodiment may also be ableto form an improved VFET by preventing performance degradation of thegate structure 330 which may occur in the previous embodiment shown inFIGS. 1A to 1C.

Meanwhile, the amount of the upper portion 331U of the gate dielectriclayer 331 which is to remain after the etching operation of FIG. 3B maybe determined such that the vertical length of the upper portion 331U ofthe gate dielectric layer 331 where the EOT increases to degrade theperformance of the gate structure 330 can be smaller than the verticalthickness of the top spacer 370.

FIGS. 4A to 4C illustrate a process of manufacturing a VFET according toyet another exemplary embodiment.

Similar to the previous embodiments, the present embodiment begins withproviding a semiconductor stack 300 shown in FIG. 4A through a CMPoperation, not being limited thereto, for further processing to completea VFET. The semiconductor stack 400 includes a bottom S/D region 410, afin structure 420, a gate structure 430 including a gate dielectriclayer 431 and a conductor layer 432, where the gate dielectric layer 432is formed of at least an interfacial layer 431-1 and a high-κ dielectriclayer 431-2. The semiconductor stack 400 further includes an interlayer440, a mask layer 450, and a bottom spacer 460. Since the materials,structures, and functions of the above elements included in thesemiconductor stack 400 may be the same as those included in thesemiconductor stacks 100 to 300, duplicate descriptions thereabout areomitted.

Further, an etching operation of the present embodiment shown in FIG. 4Bis similar to that of the previous embodiment shown in FIG. 2B. That is,an etching operation is performed on the semiconductor stack 400 toremove the gate dielectric layer 431 and the conductor layer 432, bydifferent depths from a top surface of the gate structure 430, and themask layer 450, by which an upper portion 420U of the fin structure 420and an upper portion 431U of the gate dielectric layer 431 formed alongthe upper portion 420U of the fin structure 420 take a form ofprotrusion from a plane where a top surface 432T of the conductor layer432 is positioned between the interlayers 440. After this etchingoperation, a top surface 431T of the gate dielectric layer 431 iscoplanar or substantially coplanar with a top surface 420T of the finstructure 420.

Next, referring to FIG. 4C, an epitaxy 480 is grown on the top surface420T of the fin structure 420 in the state where the fin structure 420is laterally enclosed by the gate dielectric layer 431, whereby theepitaxy 480 is grown in an upward direction and extend to an upperportion of the interlayer 440 to form an air gap spacer 470 below theepitaxy 480 and above the conductor layer 432 and between the gatedielectric layer 431 and the interlayer 440. Here, the air gap spacer470 may function of sealing the high-κ dielectric layer 431-2 as a topspacer of the VFET in the present embodiment. The epitaxy 480 may be asemiconductor epitaxy formed of formed of a material such as silicon(Si), germanium (Ge), silicon germanium (SiGe), and/or asilicon-containing material, not being limited thereto. Later, theepitaxy 480 is to be doped by one or more dopants to form a top S/Dregion in a following operation (not shown).

Since the growth of the epitaxy 480 generates the air gap spacer 470 ata side of the gate dielectric layer 431 and above the conductor layer432 instead of a top spacer having a dielectric constant greater thanair, possible parasitic capacitance occurring between a top S/D region,a top spacer and a gate structure may be reduced, thereby improvingperformance of a VFET formed by the present embodiment.

The foregoing is illustrative of exemplary embodiments and is not to beconstrued as limiting thereof. Although a few exemplary embodiments havebeen described, those skilled in the art will readily appreciate thatmany modifications are possible in the above embodiments withoutmaterially departing from the inventive concept.

What is claimed is:
 1. A method for manufacturing a vertical fieldeffect transistor (VFET), the method comprising: providing a stack of abottom source/drain region, a fin structure, and a gate structure on aside wall of the fin structure, an interlayer on a sidewall of the gatestructure, and a mask layer on the fin structure, the stack furthercomprising a bottom spacer on the bottom source/drain region and belowthe gate structure and the interlayer, and the gate structure comprisinga gate dielectric layer on a sidewall of the fin structure and aconductor layer on the gate dielectric layer; etching the stack from atop surface thereof to remove the gate dielectric layer and theconductor layer, by different depths from the top surface thereof, andthe mask layer such that an upper portion of the gate dielectric layeris positioned above a plane where a top surface of the conductor layeris positioned; and forming a top source/drain region on a top surface ofthe fin structure, a top surface of the gate structure and a sidewall ofthe interlayer.
 2. The method of claim 1, further comprising forming atop spacer at least on the conductor layer and between a sidewall of theupper portion of the gate dielectric layer and the sidewall of theinterlayer.
 3. The method of claim 2, wherein the top surface of thegate dielectric layer is positioned at the same or substantially samelevel as, or positioned lower than a level of a top surface of the topspacer.
 4. The method of claim 2, wherein the top spacer is formed of amaterial having a dielectric constant value less than 3.5.
 5. The methodof claim 2, wherein the top spacer is further formed on the top surfaceof the gate dielectric layer so that the top surface of the gatedielectric layer is positioned lower than the top surface of the topspacer, and higher than the top surface of the conductor layer.
 6. Themethod of claim 2, wherein the upper portion of the gate dielectriclayer, on which the top spacer is formed, is laterally thicker than alower portion of the gate dielectric layer having a uniform orsubstantially uniform lateral thickness along the lower portion of thesidewall of the fin structure.
 7. The method of claim 6, wherein thelateral thickness being greater at the upper portion of the gatedielectric layer is caused by at least oxidation on the gate dielectriclayer.
 8. The method of claim 2, wherein the gate dielectric layercomprises: an interfacial layer conformally formed on the sidewall ofthe fin structure; and a high-κ dielectric layer conformally formed onthe interfacial layer except at a position where the high-κ dielectriclayer is extendedly formed on a top surface of the bottom spacer.
 9. Themethod of claim 8, wherein the interfacial layer comprises at least oneof silicon oxide (SiO), silicon dioxide (SiO₂), and silicon nitride(SiON), and wherein the high-κ dielectric layer has a dielectricconstant value greater than 7 and comprises a metal oxide of or a metalsilicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, or a combination thereof.10. The method of claim 9, wherein the high-κ dielectric layer has thedielectric constant value greater than 15, and comprises at least one ofHfO₂ and HfSiON.
 11. The method of claim 2, wherein the top surface ofthe gate dielectric layer is positioned at the same or at thesubstantially same level as a top surface of the fin structure, andwherein the forming the top source/drain region comprises growing anepitaxy from above the top surface of the fin structure to extendupwardly and toward the interlayer such that an air gap spacer is formedas the top spacer below the epitaxy, above the conductor layer, andbetween the interlayer and the gate dielectric layer.
 12. A method formanufacturing a vertical field effect transistor (VFET), the methodcomprising: providing a stack of a bottom source/drain region, a finstructure on the bottom source/drain region, and a gate structure on aside wall of the fin structure, the stack further comprising a bottomspacer between the bottom source/drain region and the gate structure,and the gate structure comprising a gate dielectric layer and aconductor layer sequentially stacked on a sidewall of the fin structure;etching the stack from a top surface thereof to remove the gatedielectric layer and the conductor layer, by different depths from thetop surface thereof, such that an upper portion of the gate dielectriclayer is positioned above a level where a top surface of the conductorlayer is positioned, and such that the top surface of the conductorlayer is exposed from the gate dielectric layer; and forming a topsource/drain region on the top surface of the fin structure.
 13. Themethod of claim 12, wherein, after etching the stack, the upper portionof the gate dielectric layer is laterally thicker than a lower portionof the gate dielectric layer, on which the conductor layer is formed.14. The method of claim 13, wherein a lateral thickness of the upperportion the gate dielectric layer increases in an upward direction fromthe lower portion of the gate dielectric layer.
 15. The method of claim13, wherein the lower portion of the gate dielectric layer has a uniformor substantially uniform lateral thickness along a lower portion of thesidewall of the fin structure.
 16. The method of claim 12, furthercomprising forming a top spacer on the top surface of the conductorlayer, wherein the top source/drain region is formed on a top surface ofthe top spacer.
 17. The method of claim 12, wherein the stack furthercomprises an interlayer on a sidewall of the gate structure, and whereinthe forming the top source/drain region comprises growing an epitaxyfrom above the top surface of the fin structure to extend upwardly andtoward the interlayer such that an air gap spacer is formed between thefin structure and the interlayer and between the conductor layer and thetop source/drain region.
 18. A method for manufacturing a vertical fieldeffect transistor (VFET), the method comprising: providing a stack of abottom source/drain region, a fin structure on the bottom source/drainregion, and a gate structure on a side wall of the fin structure, thestack further comprising a bottom spacer between the bottom source/drainregion and the gate structure, and the gate structure comprising a gatedielectric layer and a conductor layer sequentially stacked on asidewall of the fin structure; etching the stack from a top surfacethereof to remove the gate dielectric layer and the conductor layer, bydifferent depths from the top surface thereof, such that an upperportion of the gate dielectric layer is positioned above a level where atop surface of the conductor layer is positioned; and forming a topsource/drain region on the top surface of the fin structure, wherein,after etching the stack, the upper portion of the gate dielectric layeris laterally thicker than a lower portion of the gate dielectric layer,on which the conductor layer is formed.
 19. The method of claim 18,wherein a lateral thickness of the upper portion the gate dielectriclayer increases in an upward direction from the lower portion of thegate dielectric layer.
 20. The method of claim 18, wherein the lowerportion of the gate dielectric layer has a uniform or substantiallyuniform lateral thickness along a lower portion of the sidewall of thefin structure.